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15

The answer to this is surprising: We are. And many (if not all) other galaxies. And they move faster than light. See, the universe is expanding, at an accelerating rate. The fabric of spacetime itself stretches out, so that galaxies seem to move away from each other. The interesting thing is that relativity does not forbid these from moving away faster ...


12

The Hubble expansion has no bearing whatsoever on the length of the year. This is because the whole Milky Way galaxy (and in fact most galaxies, if not all, and even local groups) has decoupled from the Hubble flow long ago. In fact, it could only form after it decoupled. Note that M31, our sister galaxy, is in fact falling onto the Milky Way rather than ...


12

Gravitational lensing is the effect that large amounts of gravity have on the path of light. Here's an example of the effect: The animation shows a black hole passing in front of a galaxy (simulated). In theory any object with a surface mass density larger than the critical surface mass density would be able to produce similar such effects. What's ...


12

There is also another mediator particle which moves at the speed of light other than the photon. This is the gluon, which is the exchange particle for the strong force. The odd thing about the gluon is that it's never seen by itself (that is, outside of collections of other gluons). Also, though neutrinos do in fact have mass, they are neutral particles. ...


12

The answer to the headline question is: No. Most of Saturn's rings are below the Roche limit of about 2.5 Saturn radii. Hence tidal forces will prevent that part of the rings to form a (large) moon. Actually, part of the rings may be caused by loss of material from some of Saturn's moons, as suspected from observations of Enceladus. Accretion of Earth is ...


11

Absolutely possible. There's nothing magical about a black hole. The gravitational pull of a black hole reaches as far as gravity would for another object of the same mass. If you replace the Sun with a black hole of the same mass, everything would continue to orbit it just as it currently does. Anything with mass has a gravitational force itself, and a ...


10

Yes, the moon is moving away from Earth at around 1.48" per year. According to the BBC: The Moon is kept in orbit by the gravitational force that the Earth exerts on it, but the Moon also exerts a gravitational force on our planet and this causes the movement of the Earth's oceans to form a tidal bulge. Due to the rotation of the Earth, this tidal ...


10

Gravitational lensing is the bending of light by massive objects in between the observer (us), and a background source of light. It is a direct prediction of Einstein's theory of General Relativity, and was tested and confirmed by Sir Aurther Eddington during the famous Solar exlipse of May 29, 1919, where the apparent position of a star very close to the ...


10

The tail of a comet is not actually "slowing down and falling away" from the comet, like you might expect to see when smoke streams out from behind a moving object on earth. The tail of a comet is actually being pushed away from the sun by the solar winds and radiation. That's why the tail of a comment always points away from the sun, and doesn't stream out ...


9

When an object is in orbit, there are two factors at play, not just one. The first, as you mention, is the force of gravity pulling the objects together. However, each object also has a momentum component which is generally (in the case of circular orbits) perpendicular to the direction of the gravity. If we look at the common situation of a small-mass ...


9

Hmmm no, it wouldn't be cluttered with debris, and yes, it's a good idea to park the JWST (James Webb Space Telescope) at the Sun-Earth L2 point. The five Lagrange points are unstable, for one because of the gravitational anomalies of the two massive bodies of the Lagrange system, eccentric orbits, and there are many other factors to their instability. At ...


9

(Disclaimer: As I already pointed out in a comment to the question above, I never did a calculation with $H_0$ before and I might be utterly, horrible wrong with my interpretation.) If you completely ignore the slowly changing orbit of earth and only take expansion of space into account and assume the Hubble-parameter to be pretty constant in the timeframe ...


9

There are plenty of rapidly moving objects in astrophysics. A good place where one can get moving relativistically is near an event horizon of a black hole. A simple Newtonian estimate illustrates the point. Black hole has all its mass $M$ hidden under an event horizon of the radius of order $r_{g}=\dfrac{2GM}{c^2}$. An object moving circularly in the ...


9

The first question as stated has a rather trivial answer: "If the sun magically disappeared, instantly, along with all its influences, how long would it take its gravity to stop having an effect on us?" Since the Sun's gravity is among its influences, it would instantly stop having an effect on us. That's just part of the magical situation, and doesn't ...


8

Yes - this is the formula: $$F = G\frac{m1 * m2}{r^2}$$ Using this equation, we can say that all atoms in the universe exert force upon eachother. One carbon-12 atom has a mass of $1.660538921(73)\times10^{-27} kg$. That's a crazy small mass. Now let's say that these two atoms are 100,000,000 light years apart. That's $9.461\times10^{23} m$, which is a ...


8

Gravity doesn't affect the speed of light. It affects the space-time geometry and hence the paths of light. However, this can have a similar effect. Light emitted at source $S$ to pass a massive object $M$ that is very close on the otherwise (if M weren't there) straight path to an observer $O$ has to "go around" $M$, which takes longer than following the ...


8

What is the difference between time and space-time? Space-time is time plus space. How does gravity affect the passage of time? The higher the gravity of a planet or star and the closer to that body the slower the time. What is the speed of light and how does it relate to time? The speed of light is 299,792.4580 km/s in vacuum, the speed at ...


8

In a car, you have a perception of speed because of (a) the "wind" passing by as you rush through the air which is not moving at the same speed as the vehicle, and (b) you perceive the stationary objects nearby as "moving" off into the distance behind. As the earth moves in its orbit, you don't notice any "wind" from the planet rushing through space, as the ...


7

There are other formulas at work, but not any other forces. You need to take into account ont only the force, thus the acceleration, but also the current velocity of a body orbiting another. To put it simply: if you move a ball sticked to a rope around your head, the only forces are the tension of the rope and gravity towards the floor. Ignoring gravity, ...


7

Reason 1: Let's look at the Friedmann equations without the cosmological constant. $$ \frac{\dot{a}^2 }{a^2} = \frac{8 \pi G \rho}{3}-\frac{kc^2}{a^2}$$ The term on the LHS is just the Hubble constant squared $H^2$ which can be measured the direct measurement of recession velocity of galaxies The density term can be said to be a combination of ...


6

As Walter says, gravity doesn't bend light. Light travels along null geodesics, a particular type of straight path. Since (affine) geodesics don't change direction by definition, geometrically light trajectories are straight. Moreover, the speed of light in vacuum is $c$ in every inertial frame, regardless of whether or not spacetime is curved, although a ...


6

The strength of the Earth's gravitational field compared to the Moon and the Sun is not enough to capture and hold satellites - there are too many disruptive forces that would rip them away over time. However there are some objects at the Lagrangian points - the points where the gravitational fields of the Earth and other objects are equal and so it is ...


5

There are certainly people who study alternative (non-General Relativistic) theories of gravity. The most popular theories have so far been: Modified Newtonian Dynamics (MOND) - which essentially postulates that Newtonian Mechanics break down on some scale, leading to the rotation curves we see in galaxies. Tensor–vector–scalar gravity (TeVeS) - this is a ...


5

All objects in the universe exert a gravitational force on all others - the farther away an object is, the smaller is the force it exerts. (The force is inversely proportional to square of the distance from the object, so an object twice as far away means only 1/4 the amount of force). Furthermore, the more massive the object, the greater the ...


5

From a (more) physics standpoint our acceleration on earth is basically zero from what we can feel. Just like the others that posted about cars traveling at a certain constant velocity, you won't feel a change. If a car is traveling at a constant velocity there is essentially no feelable force acting on your body. Therefore you you don't feel any effects of ...


5

What I ask myself is: Couldn't there be "negative" bundles of mass just the other way that pushes matter away instead of invisible dark matter that pulls it? The galaxy rotation curve indicates a (positively massed) dark matter distribution that is close to spherically symmetric; cf. dark matter halo. I take it that you are asking whether instead of ...


5

If by "a hollow object" you mean a spherical shell -- a theoretically perfect sphere Moon, with a perfect sphere of material removed from the center: The center of mass, and therefore the center of gravity remains at the geometric center. Ref Newton's Law; Bodies with spatial extent. The body of the moon is plastic; Meaning the gravitational forces are ...


5

(I will assume a Schwarzschild black hole for simplicity, but much of the following is morally the same for other black holes.) If you were to fall into a black hole, my understanding is that from your reference point, time would speed up (looking out to the rest of the universe), approaching infinity when approaching the event horizon. In ...


5

Dark matter, is just a name for something we know nothing of. It was named to account for an extra gravity source for which there have been indirect observations, but yet we cannot explain. The force of gravity exerted by light is negligibly small yet we have measured the gravitational pull of Dark Matter to be big enough to affect whole galaxies; it is ...



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